Hi All

I've had a situation a few times where when shifting quickly under heavy acceleration from 4th to 5th it won't drop into gear, and then it locks out - you can't get 6th or 5th or back to 4th, it feels like it jams at the gate. Drop it back into neutral, lift clutch, depress clutch and pray and it will go into 4th, then shift normally again from then on.

I bought it used as with supposed low mileage, it's an NB2 box as it has the later larger shifter bushing. Normal gentle shifts are fine throughout all the gears, it's only if you rush the gearchange a bit when WOT that it gets itself confused.

Any suggestions? Slightly bent selector fork, weak detente spring on reverse meaning it's going across too far, or just the driver being a ham fisted fucktard?

 

Ham fists. The only real way to fix the 6 speed shifter feel is the MiataRoadster shifter kit. It's expensive but cheaper than a money shift. This isn't a cure all thought and if you really try to send it into 5th you'll still experience the same thing.

 

5th isn't as far to the right as the shifter will move. Going too far right will lock it out of moving forward. MR shifter gives you better feel but won't solve the problem entirely, just makes it easier to find.

 

Has anyone tried the CAE shifter for the 6 speed? These are highly rated in Europe but I've not read anyone's opinion that I trust on why or even how it is better.

https://cae-racing.de/CAE-Ultra-Shif...-NB-19-mm-ball

 

I can see why you don't want to be the first one to try it - HOW MUCH???

Looks to be a lovely bit of engineering though, but €799?

Thanks for the feedback, I'll start saving for the MR kit and look to be less of a 'tard in the future...

 

I found the stock shift **** too light for how notchy the 6 speed is. Swapping to a heavier **** helped immensely. If you are only having issues at WOT and are still on the stock motor mounts/diff mounts then the movement of the motor/transmission are probably also at play.

 

I have stock diff mounts with void fillers. I was on the Mazdaspeed mounts, but have recently swapped to the Supermiata Hybrid mounts as part of the trying to help with this issue.

I've not driven it that much since so not fluffed a shift, but now something rattles behind the dash and drives me nuts

 

I had this problem for 2 seasons. When it got hot it would start to randomly lockout 5th gear. So I'd be a few laps into an afternoon session and I'd try to grab 5th and nothing. It felt like you missed the gate. I'd be coasting down the straight with the clutch pushed in trying to find the damn gear. I could usually go into 6th or back down to 4th since I dropped so much speed, but at that point I'm flustered and concentration is shot.

Ended up rebuilding the box this winter due to 3rd gear syncho being toast. At that time I replaced the 5th/rev shift fork and clutch hub along with all the synchros. Zero issues now.

 

I've been struggling with 4th to 5th (and 5th to 4th). I thought it was my gearbox getting too hot, and that the problem would be manageable with a cooler. Anyway, with my cooler, 4th to 5th is no better..

I think the reverse lockout spring isn't stiff enough, so going up and across from 4th to 5th, I can go too far across, effectively to 7th, but there's obviously no gear there.

It's also pretty unnerving going from 5th to 6th, as I can catch the edge of the reverse gate.

I'd pay half the price of the CAE shifter for something that would properly lock out the reverse gate but I'm not keen on paying 1/4 of a BMW trans swap for one. Though the CAE has integrated centering springs so would help with 5th to 4th too....

https://cae-racing.de/CAE-Ultra-Shif...-NB-19-mm-ball

 

I put the miataroadster short shift kit in, along with their brass super heavy **** - it's helped a lot, and the shift on the 6 speed box is a lot better.

It is still possible to try and get '7th' as you say, but the increased effort means it's harder to overcome the reverse gate spring so I do it less often...

 

I just saw this thread and thought I'd give an update:
I rebuilt my AZ6 last winter due to 3rd gear grind, reverse was a real struggle to engage, and also randomly get the 5th gear lockup.
I replaced all the synchros, shift forks, and all the small parts and it was working grreeeaaat. I also installed a Supermiata 5.5lb twin disk and a Miata Roadster shifter. Synchros were absolutely toast on 3rd and rev; like zero braking force on the gear cone.

Anyways, I ran 4.5 NASA events without a single issue. Then I had a BIG off at Mid Ohio at China Beach during the 1st session on Sunday. A jackass in a 350z blew his engine and stayed on line while oiling 75% of the track. You could follow the trail of oil back to his paddock spot. Stupid ain't cheap... Well, I hit the brakes at China Beach and the tires locked and nothing else happened, so I made it about 3/4 of the way through the gravel trap. This shredded the DEI titanium wrap on my header. I somehow managed to not get stuck in the gravel and got it back to the paddock. There was no chance I was pulling the header to reinstall the wrap at the track, so I just hacked all the shredded part off (the entire bottom section, which is the closest to the trans). I then went out and got a 5th gear lockup on the back straight in the afternoon session (August Mid Ohio).

Based on this, I'm 99% sure the lockout is due to trans temps. I've added a temp sensor, which I plan to log for next season.

 

It warms my heart to know I'm not the only one that isn't allowed into 6th gear sometimes. Oddly enough, my issue with it is at partial throttle, and never at wide open.
It still happens, but less often with a bronze bushing, old 5 speed **** and comp mounts.

 

5th and reverse are on the same shift fork. I've found that the bushings inside of the fork (there are two small ones) can start to move their way out and cause issues. I had a trans that the bushing was so far outside the fork (without coming loose) that I couldn't engage R at all. I had all 6 forward gears though. Made for an interesting track weekend.

 

I'm still struggling a lot with this. Feels like it's getting worse. I've driven 2 other NB2 6 speeds and both of those were fine.

It seems more than just that I'm trying to engage 7th. It feels like its locked out of 5th randomly, but other times it's fine. It was quite a pain yesterday at Silverstone GP circuit needing to do the 4th to 5th shift 6 times round a lap. In the end, I was leaving it in 5th for a lot of them and just riding the torque.

 

I think there’s several problems to address. I suggest starting with heat gains from exhaust. Metal shields do wonders to keep that in check. Next is driver technique. Elbow up, open palm helped a ton. That should get you through most DE/Race sessions. Trans cooler will help by limiting expansion growth of aluminum shift forks. I feel like that’s what I fought the most when trans got hot. Had to really slow shifting and concentrate more. Even then sometimes it would just not want to go into 5th.

When racing there are tons of variables running through your mind. Shifting should not be one of em. In an ideal world I’d have a fresh trans rebuild, CAE shifter (that reverses gate is a bitch!) and trans cooler.

In a really ideal world it’s a sequential trans.